1. Field of the Invention
The present invention relates to a method and apparatus for preventing a surging of a vehicle having an internal combustion engine. Such a surging is often due to variations in a cycle-to-cycle combustion in an internal combustion engine.
2. Description of the Related Art
Generally, a vehicle having an internal combustion engine is driven by the torque generated by the internal combustion engine, and when the torque is intermittently lost or an negative torque is generated by a misfiring of the internal combustion engine, the vehicle is affected by a negative acceleration force. A repetition of such a negative acceleration force causes a longtitudinal vibration of the vehicle, i.e., surging, and passengers in the vehicle suffer discomfort. Therefore, it is desirable to reduce the surging of a vehicle due to variations in the combustion cycle of the internal combustion engine.
Unexamined Japanese Patent application No. 58-160530 discloses a method of controlling the torque of the internal combustion engine to reduce variations in the torque by detecting these torque variations. In this method, torque variations are detected by at least one driving parameter of the engine such as a variation of the rotational speed of the engine, a longtitudinal acceleration of the vehicle, a variations of the combustion pressure of the engine, or a torsion angle of a transmission axis of the engine, and the detected torque variation is limited by a filter allowing the passage of specific vibration frequencies having bodily affects. Accordingly, in this method, vibration frequencies having a bad effect on the human body are selected by the filter from among the variety of longtitudinal vibration frequencies of the vehicle, and in accordance with the detection of such vibration frequencies, variations of the torque of the engine are determined to have occurred and the torque of the enguine is then controlled to reduce the detected torque variations.
Nevertheless, when the vehicle is traveling on a rough road surface, the roughness of the road surface is picked up by the tires of the vehicle as a vibration, and this vibration may cause the vehicle to vibrate longtitudinally; which longtitudinal vibration may be erroneously detected as surging according to th the method disclosed in Unexamined Japanese Patent application No. 58-160530. Namely, in this method, if the frequency of the longtitudinal vibration caused by the vehicle traveling on a rough road surface contains frequencies of 1 to 10 Hz, which agrees with specific vibration frequencies having bodily affects, these frequencies of 1 to 10 Hz are attributed to surging caused by variations of the combustion cycle of the engine, and thus the torque of the engine is controlled in the wrong direction and the surging erroneously increased. The probability of detecting vibration due to a rough road surface as surging is higher when the vehicle is traveling on an uneven road surface which causes a continuous and periodical longtitudinal vibration of the vehicle.
Further, the outer circumferences of the tires of the vehicle are not a ture circle and are, in practice, distorted from that shape, and as a result, the vehicle may vibrate in accordance with the rotation of the tires to thereby produce a primary rotational vibration at the tires. In this case, if a frequency of the primary rotational vibration at the tires matches a frequency of the natural vibration of a vehicle driving system, the vehicle driving system is resonated and this resonance is detected as a vibration caused by surging, whereby the torque of the engine is controlled in a wrong direction to thereby erroneously increase the surging.